In the field of integrated circuits, in order for the integrated circuit chip to be mounted into its end equipment, and in order for conventional solder connection to be made to the integrated circuit chip, packages are used to house the integrated circuit chip. These packages, such as the well-known dual-in-line (DIP) packages, leadless chip carriers, pin-grid array packages, and other conventional packages, each have leads or terminals which can be connected to a printed circuit board or other piece of equipment. Within the package, connection is made, generally by way of wire bonding, between the external leads or terminals of the package and the integrated circuit chip itself.
Even for the short length between the external terminals of the package and the integrated circuit chip, via the wire bond and the run within the package body from the lead finger to the external terminal, parasitic inductance is present. The high switching speeds of modern digital circuits result in relatively high levels of instantaneous current required to perform the switching operation. The rate of change of current required from a power supply to effect the switching will, due to the presence of finite inductance from the package run and the bond wires, as well as from any external wires or other conductors connected to the power supply terminals of the packaged integrated circuit, result in modulation of the power supply voltage since the current through an inductor cannot change instantaneously. The modulation of the voltage will, of course, be equal to the product of the inductance and the time rate of change of the current through the conductor. This modulation of the power supply voltage, commonly referred to as power supply noise, can upset the operation of the integrated circuit if it is of sufficient magnitude.
Other causes of power supply noise include the exposure of the integrated circuit to transient radiation. A transient radiation event will cause normally off MOS transistors to conduct from source-to-drain in a manner equivalent to photoconduction (i.e., generation of electron-hole pairs). Due to the nature of the transient radiation event, the net current of the generated electrons traveling to the positive power supply and of the generated holes traveling to ground will have a large time rate of change. Similarly as the time rate of change of the switching current of the circuit, the time rate of change of the current due to the transient radiation event will result in modulation of the power supply potential from the inductance of the power supply leads. In an integrated memory circuit such as a static RAM which is exposed to such a transient dose, if the noise due to the photoconduction is of sufficient amplitude to cause the power supply voltage to drop below a certain level, this noise, or sag, may cause loss of the data stored in the static memory cells.
Prior techniques to reduce power supply noise from internal operation, as well as from external sources such as transient radiation, have included the connection of decoupling capacitors between the power supply terminals external to the integrated circuit package. Another prior technique has been the connection of small capacitors within the cavity of the integrated circuit package. In this prior technique, the connection of the capacitor to power supply leads of the package has been made by providing connection internal to the package header between the external leads and pads located within the package cavity, so that the capacitor can be mounted within the cavity in such a manner that both plates are connected to the pads in the cavity. Connection between the header and the chip is made directly by wire bonds, in the same manner as would be made if the capacitors were not present. While such decoupling capacitors are effective in reducing the magnitude of the noise or sag, significant parasitic inductance still remains between the external terminal and the integrated circuit chip, so that noise and sag from these causes may still affect the operation of the circuit.
It is therefore an object of this invention to provide decoupling capacitors as close as possible to the integrated circuit chip within a package.
It is yet another object of this invention to provide such capacitors which are assembled within the package using the same techniques as used for assembling the associated integrated circuit chip within the package.
It is yet another object of this invention to provide such capacitors which provide bond wire connection to the integrated circuit chip, so that the decoupling capacitors are physically connected between the header leads and the integrated circuit chip.
Other objects and advantages of the invention will become apparent to those of ordinary skill in the art having reference to the following specification in conjunction with the drawings.